Carrier Screening Information

Carrier screening is a genetic testing approach used to determine whether an individual or couple carries pathogenic variants associated with inherited genetic disorders, such as cystic fibrosis, spinal muscular atrophy (SMA), or sickle cell disease. Carriers are typically asymptomatic but may pass disease-causing variants to their children.

Humans have two copies of each gene, one inherited from each parent. Most conditions identified through carrier screening follow an autosomal recessive or X-linked inheritance pattern, meaning disease occurs only when both gene copies are affected in the case of autosomal recessive, or only when the X chromosome is affected in the case of X-linked conditions.

When both partners are carriers of the same autosomal recessive condition, there is a:

• 25% chance of an affected child
• 50% chance of a carrier child
• 25% chance of an unaffected, non-carrier child

Carrier screening is performed using blood, saliva, or a buccal swab and falls into two main categories:

Biochemical (enzyme-based) screening

This method measures enzyme activity linked to specific genetic disorders. While still used for select conditions such as Tay-Sachs, enzyme screening has limited sensitivity and may fail to identify some carriers with rare variants.

Molecular genetic screening

Molecular testing, including PCR, microarray, and NGS among other testing platforms, analyzes DNA directly and is now the preferred clinical standard.

• Targeted carrier screening evaluates specific genes or variants based on family history or ancestry.
• Expanded carrier screening (ECS) evaluates dozens to hundreds of genes in a single test and is now recommended for individuals of all ethnicities due to population admixture and the limitations of ethnicity-based screening.

Depending on the panel, ECS may include tens to hundreds of genes associated with severe, childhood-onset autosomal recessive or X-linked conditions.

Modern technologies such as next-generation sequencing (NGS) and microarray-based analysis enable comprehensive, efficient, and cost-effective screening by analyzing many known pathogenic variants simultaneously using a single sample.

Next-generation sequencing (NGS) is the most widely used technology for expanded carrier screening panels.¹

While both microarray and NGS technology allow for robust workflows and customizable panels, NGS enables simultaneous sequencing of dozens to hundreds of genes in a single assay, allowing for broad detection of pathogenic variants across diverse populations. Compared with targeted genotyping or enzyme-based methods, NGS offers several key clinical advantages:

• Higher detection rates: NGS identifies a wider range of pathogenic variants, including rare and population-independent variants that may be missed by targeted or ethnicity-based panels.
• Comprehensive gene coverage: NGS interrogates entire coding regions and clinically relevant regions, rather than a limited set of predefined variants.
• Reduced residual risk: Broader variant detection lowers residual risk after a negative result, improving the clinical utility of screening.
• Scalability and efficiency: Multiple genes and conditions are analyzed simultaneously using a single sample, streamlining laboratory workflows, and reporting.
• Equitable screening across ethnicities: NGS-based expanded carrier screening reduces reliance on self-reported ethnicity and improves risk assessment in increasingly blended populations.
• Compatibility with reproductive care pathways: NGS results may easily be integrated with genetic counseling, IVF planning, and preimplantation genetic testing (PGT) strategies.

As sequencing costs continue to decline and bioinformatic interpretation improves, NGS has become a cost-effective and clinically robust solution for identifying carrier status and supporting informed reproductive decision-making.

Carrier screening enables clinically actionable information that supports informed reproductive decision-making. It is particularly valuable for couples with a family history of genetic disease and for identifying risks that may not be apparent based on ethnicity alone.

When combined with genetic counseling, carrier screening empowers intended parents and care teams including clinical geneticists, obstetrician-gynecologists, and reproductive endocrinologists to proactively manage genetic risk and align reproductive strategies with patient goals.

Who should consider carrier screening?

Carrier screening is recommended for all individuals or couples planning a pregnancy or currently pregnant, regardless of ethnicity or family history. It is especially important for couples undergoing fertility treatment or assisted reproductive technologies.

When is the best time to perform carrier screening?

Preconception screening is preferred, as it provides the widest range of reproductive options. However, screening can also be performed during the first trimester of pregnancy if preconception testing was not completed.

What conditions are typically included in expanded carrier screening?

Expanded carrier screening panels commonly include conditions such as cystic fibrosis, spinal muscular atrophy, hemoglobinopathies, and many other severe, early-onset genetic disorders. Panel content varies by test and may include conditions across multiple ethnic populations.

What happens if both partners are carriers of the same condition?

If both partners are carriers, referral to a genetic counselor is recommended to discuss reproductive options, which may include IVF with preimplantation genetic testing (PGT), use of donor gametes, or prenatal diagnostic testing.

Why is expanded carrier screening preferred over ethnicity-based screening?

Ethnicity-based screening can miss at-risk couples due to mixed ancestry and incomplete self-reported ethnicity. Expanded carrier screening provides more equitable and comprehensive risk assessment across diverse populations.

How accurate is carrier screening?

Molecular carrier screening has high analytical sensitivity and specificity; however, no test detects all possible pathogenic variants. Residual risk remains even after a negative result and should be communicated during genetic counseling.